The present invention relates generally to electron generating devices including field emission displays, and more particularly, to a method for treating emitter tips to reduce their electron work function.
A device which utilizes field emission cathode tips to produce individual beams of current is described with respect to FIG. 1. FIG. 1 shows a plan view of the device having a substrate 100 with emitter tips 102a-102n formed thereon. The device also has a gate electrode 104 which is separated from the substrate 100 by an insulating layer 106. When a voltage 108 is applied between the gate electrode 104 and the substrate 100, an electric field is created which causes emitters 102a-102n to emit electrons 112 as shown. Electrons 112 then strike faceplate 110. Faceplate 110 typically has formed thereon a plurality of phosphor dots which are illuminated by the electrons 112.
Devices of the type just described are especially suitable for use in electronic applications requiring small, flat video displays such as lap top computers and video recorders. However, these types of devices are often battery operated. Therefore, it is important that the electronic components used in these devices, including the displays, consume as little power as possible in order to preserve battery life. This problem is especially compounded because it is generally desired that these devices are constructed to weigh as little as possible, and so, it is impractical to provide extended battery operation by using larger and heavier batteries. Therefore, it is important that any display designed for use with such devices consume as little power as possible.
With devices of the type described above, the amount of energy needed to cause the emitters 102a-102n to emit electrons 112 is known as the "work function" of the emitter. The greater the work function, the more energy required to cause the emitters to operate. Thus, it is desirable to create emitters having the lowest possible work function.
Previous attempts to create emitters having a low work function have not been completely satisfactory. For example, in U.S. Pat. No. 5,089,292 (incorporated herein by reference) claims a method of coating the surfaces of an array of emitter tips with a layer of material, for example, cesium, which is said to reduce the electron work function of each of the emitter tips.
However, the above method does not recognize that the work function of the emitters is increased due to the formation of native oxides or other layers that are formed on the emitters during processing. Methods which attempt to reduce the work function of the emitter by coating it with another material simply coat over emitters having a high work function due to the problems described, and do not address the underlying problem. Accordingly, it is an object of the present invention to overcome the above-mentioned problems.